Air conditioning control system



Feb. 24, 1942. B. MILLER ETAL AIR CONDITIONING CONTROL SYSTEM Filed June 11, 1937 2 Sheets-Sheet 1 4 D G BTM i ller WlliamlLJd-fitu 1942- B. MILLER ETAL AIR CONDITIONING CONTROL SYSTEM Filed June 11, 1937 2 Sheets-Sheet 2 LeoB-Milla' WIIiamLJll-Grafh W fi nmw avl lllllrllllll Patented Feb. 24, 1942 AIR, CONDITIONING CONTROL SYSTEM Leo B. Miller, Hartsdale, N. Y., and William L.

McGrath, St. Paul, Minn, assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 11, 1937, Serial No. 147,694

9 Claims.

This invention relates to control systems in general and more particularly to control systems for air conditioning apparatus. 1

In the past, control systems for air conditioning apparatus have had their control instrumentalities located at various positions, such as adjacent to the conditions to which they respond, and consequently they have been widely spaced from each other and from the apparatus which they control. As a result long runs of wiring were required which necessarily increased the installation costs. Further,- the installation men were not always familiar with the control systems they were installing and it was not unlikely for them to connect up these widely spaced control instrumentalities incorrectly even though specific instructions were issued to them. This invariably caused unsatisfactory operation of the air con ditioning system. As is often the case, the control instrumentalities must be adjusted with respect to each other to make the control system operate properly and a great deal of time was expended by the installer or service men in moving from one control instrumentality to another.

, These difliculties, as well as many others, not

only caused the installation and servicing costs to remain high but also increased the possibility of errors upon the part of the service or installation men.

In application Serial No. Clarence W. Nessell on June 7, 1937, one arrangement for overcoming the above difficulties is disclosed.

It is an object of this invention to provide an improved arrangement for obviating the above difllculties whereby installation and servicing costs are reduced to a minimum and whereby the chances of error on the part of the installation or service men is also reduced to a minimum much to the benefits of the air conditioning trade and the ultimate user.

The unitary control arrangement of the above referred to Clarence W. Nessell application is composed of a group of standard instruments mounted in a common housing. Although such an arrangement reduces installing errors and installation and servicing costs, it is relatively expensive to manufacture inasmuch as it is composed of standard instruments. As will be apparent these standard instruments must be self 146,756, filed by to reduce costs of the manufacture of the unitary, control arrangement which, when taken in connection with reductions in installation and service costs, provides an extremely desirable advance in the art of automaticcontrol systems. In carrying out this object of the invention control elements or units as distinguished from standard instruments are utilized. These control elements are reduced to simple movements and by reason of their novel construction all of the hitherto known complex adjusting means are eliminated. In addition these simple control elements are constructed to be mounted on control panels, in many instances in conjunction with other control elements, and therefore they need not be self contained, enclosed in individual casings or rugged in construction, all of which leads to reduced production costs.

These simple control elements may be fabricated so as to be responsive to any desired conditions, such as, pressure, temperature, humidity, etc., and if it be desired to control an apparatus in accordance with any condition or combination of conditions, the proper control element or elements may be selected, mounted on a common panel and connected together to perform the desired control sequence. A large number of these simple control elements can be manufactured and stocked and then selected according to the control sequence desired and by reason of this mass production, production costs are further decreased. A unitary control arrangement relatively inexpensive in cost may therefore be readily fabricated to meet practically any control problem and such unitary control arrangement, containing all of the control instrumentalities, may be readily and cheaply mounted on the apparatus which it controls.

Therefore, a further object of this invention is to provide a new and novel unitary control arrangement embodying the above principles.

Another object of this invention is to provide a novel control arrangement for an air conditioning apparatus to obtain in a new and improved manner a desired sequence of control.

Other objects and advantages will become ap parent to those skilled in the art upon reference to the accompanying specification, in claims and drawings.

For a more thorough understanding of this invention, reference is made to the accompanying drawings in which Figure 1 is a sectional view taken substantially along the line |-l of Figure 2 showing one type of apparatus to which the control system of this invention may be applied,

Figure 2 is a sectional view taken substantially along the line 2-2 of Figure 1,

Figure 3 is a diagrammatic view of the unitary control arrangement of this invention,

Figure 4 is a sectional view of one of the control units taken substantially along the line 4-4 of Figure 3,

Figure 5 is a sectional view of another control unit taken substantially along the line 5--5 of Figure 3,

Figure 6 is a sectional view of still another control unit taken substantially along the line 66 of Figure 3,

Figure 7 is a partial sectional view taken substantially along the line 1-! of Figure 4 to more clearly illustrate the adjusting mechanism utilized in Figure 4.

Referring now to Figures 1 and 2 an air conditioning apparatus is generally designated at I for conditioning the air of a. space. The air conditioning apparatus I 0 is provided with a return air opening II which leads to a return air chamber I2. Located in the return air chamber I2 are fans I3 operated by an electric motor I4 for forcing return air over a cooling coil I into a delivery chamber I6. Cooled air is conducted from the delivery chamber I6 through an opening IT to the space to be conditioned. The cooling coil I5 is illustrated as being of the direct expansion type. Located below the return air chamber I2 is a chamber I8 which encloses a mechanical refrigerating apparatus. The mechanical refrigerating apparatus is shown to include a condenser I9 and a compressor 20. Compressed refrigerant is discharged by the compressor through a high pressure pipe 2| into the condenser I9 where it is liquefied. Condensed refrigerant passes through a liquid line 22 and an expansion valve 23 into the direct expansion coil I5. Expanded refrigerant is withdrawn from the direct expansion coil I5 through a suction pipe 24 by the compressor 20. Since this mechanical refrigerating apparatus is conventional a further description thereof is not considered necessary.

Also located in the chamber I8 is a partition 26 upon which is mounted the unitary control arrangement generally designated at 21. Referring now to Figure 3 the unitary control arrangement 21 is shown to comprise a common mounting structure or panel 28 upon which are mounted the various basic control elements or units. A control unit responsive to changes in space temperature is generally designated at 29, a control unit responsive to variations in suction pressure of the refrigerating apparatus is generally designated at 30 and a control unit responsive to changes in high pressure of the refrigerating apparatus is generally designated at 3I. These three control units are adapted to control a relay or starter generally designated at 32 and if desirable, this relay or starter 32 may include overload switching mechanism to provide overload protection. Power is supplied to the relay 32 by means of a step down transformer generally designated at 33. A combined manual and overload cut-out switching mechanism for controlling the operation of the fan I4 is generally designated at 34 and a switch for placing the control system in operation is generally designated at 35. Suitable terminal blocks for connecting the unitary control arrangement to the fan motor I4, a source of power, and the compressor motor 20 are generally designated at 35, 31, and 38, respectively.

Referring now to Figures 3 and 4 the space temperature responsive control unit is shown to comprise a substantially flat plate 40 on one side of which is secured a bellows assembly 4| as by screws 42. The bellows assembly 4| is connected by a capillary tube 43 to a bulb 44 located in the return air chamber I2. The bulb 44 is preferably charged with a volatile fluid so that the bellows assembly 4| is operated in accordance with changes in space temperature. The bellows assembly 4I operates a plunger 45 which engages a lever 46 pivoted at 4'! to a bracket 48 carried by the flat plate 40. A spring 49 maintains the lever 45 in engagement with the plunger 45. Resilient switch arms 5I and 52 are carried by the lever 46 and these switch arms are braced by means of brackets 53. The brackets 53 and the switch arms SI and 52 are connected to the lever 45 and to conductors 55 by screws 54. The conductors 55 are in turn connected by suitable lead wires 56 to terminals 51 mounted on an insulated block 58 secured to the plate 40 by screw 59. The switch arms 5| and 52 are adapted to engage an adjustable contact 60 and a stationary contact GI carried by brackets 62 and 63 respectively. The brackets 62 and 63 are also secured to the terminal block 58 as by rivets 64. The brackets 62 and 63 extend through the terminal block 58 and an opening 65 in the plate 40 and an opening 66 in the plate 28 allow the terminals to extend therethrough as well as the bellows assembly 4|. By reason of this arrangement the wiring connections may be made at the rear of the panel while only the switching mechanism is located on the front of the panel.

A U-shaped bracket extends forwardly from the plate 40 and is provided with a bearing 69 for a rotatable shaft 10. The shaft I0 is rigidly secured to a cup II which in turn is rigidly secured to a nut 12. The nut I2 engages a screw member I3 which is provided with four projections I4 as illustrated in Figure '7. A plate 15 is provided with suitable apertures which are engaged by the projections I4 and the plate I5 is provided with ears I6 which are adapted to slide in slots 1! located in the U-shaped member 68. The plate I5 is prevented from rotating by the ears I6 and therefore the screw member I3 is also prevented from rotating. Since the screw member I3 cannot rotate, rotation of the shaft III and the nut I2 therefore causes longitudinal movement of the screw member I3. A screw 18 screw threaded into the screw member I3 adjusts the plate 5 with respect to the screw member I3 and therefore provides means for obtaining factory calibration of the control unit. A spring I9 engages the plate I5 and also engages an abutment member which in turn engages the lever 45. A handle 82 is secured to the shaft III for causing longitudinal movement of the plate I5 and therefore adjustment of the compression in the spring 19. The spring I9 urges the switch arms 5| and 52 away from the contacts 62 and 63, respectively. Upon an increase in space temperature the bellows assembly acts against the spring I9 to move the switch arms 5I and 52 into engagement with the contacts 60 and 6|, respectively. By adjusting the compression in the spring 19 the temperature value at which the switch arm 52 engages the contact GI may be varied and also by adjusting the adjustable contact 60 the temperature at which the contact I81.

' the high pressure pipe 2|.

switch arm engages the contact 68 may be varied. Preferably, the switch arm 5| engages the adjustable contact 68 before the switch arm 52 engages the stationary contact 6|. For purposes of illustration it is assumed that the switch arm 5| engages the adjustable contact 68 when the temperature increases to 73 and the switch arm 52 engages the stationary contact when the temperature increases to 75.

Referring now to Figures 3 and 6 the suction pressure control unit 38 is shown to comprise a substantially flat plate 85 to which is suitably secured a bellows assembly 86. The bellows assembly 86 is shown to comprise a bellows 81 sealed at one end to the casing and at the other end to a movable plate 88. carries a plunger 89 in which is screw threadedly mounted an abutment 98 for engaging a lever 9|. The lever 9| is pivoted at 92 to a bracket I I2 carried by the plate 85 and a spring 93 urges the lever 9| into engagement with the abutment 98. A spring 94 is located between the movable plate 88 and an adjusting nut 95. By suitably rotating the nut 95 the compression in the spring 94 may be varied. The bellows assembly 86 is connected by a pipe 98 to the suction pressure pipe 24 of the mechanical refrigerating apparatus. The lever 9| carries resilient switch arms 91 and 98 which are braced by brackets 99. The switch arms 91 and 98 and the brackets 99 are secured to the lever 9| and to conductors I8I by screws I88. The conductors I8I are electrically connected by lead wires to terminals I83 carried by an insulating block I04 which in turn is secured to the plate 85 by screws I85. The switch arms 81 and 98 are adapted to engage contacts I86 and I81, respectively. The contacts I86 and I81 are carried by brackets I88 which extend through the terminal block I84 and are secured thereto by means of rivets. Preferably, the contact I88 is made adjustable. The plate 85 and the panel 28 are provided with apertures H8 and III to accommodate the terminals of the terminal block I84 wherebyall of the wiring connections may be made at the rear of the panel 28. The aperture III also accommodates the bellows assembly 86. Upon an increase in suction pressure the movable plate 88 is operated against the action of the spring 94 to move the switch arm 91 into engagement with the adjustable contact.|86 and to move the switch arm 98 into engagement with the stationary contact I81. Preferably, the switch arm 91 engages the contact I88 before the switch arm 98 engages the For purposes of illustration it is assumed that the switch arm 91 engages the contact I86 when the pressure increases to pounds and the switch arm 98 engages the contact I81 when the pressure increases to pounds.

In Figure 5 the high pressure responsive control unit 3| is shown to comprise a substantially flat plate II 5 suitably secured to the panel 28. A bellows assembly H6 is secured to the plate II5 and is provided with a pipe II1 leadingto The bellows assembly II6 operates a plunger H8 in which is screw threadedly mounted an abutment II9 for engaging a lever I28 pivoted at I2I to a bracket I22 carried by the plate II5. A spring I23 maintains the lever I28 in engagement with the abutment I I9. A nut I24 adjusts a spring located in the bellows assembly for adjusting the pressure setting of the control unit. The lever I28 carries resilient switch arms I25 and I26 which are The movable plate 88' braced by brackets I21. The switch arms I25 and I26 and the brackets I21. are secured to the lever I28 and' to conductors I29 by screws I28. The conductors I29 are connected by lead wires to terminals I3I carried by a terminal block I32 mounted on the plate II5 by screws I33. The switch arms I25 and I26 are adapted to engage contacts I34 and I35, respectively. The contacts I34 and I 35 are carried by brackets I36 and I31, respectively, which extend through the terminal block I32 and which are connected thereto by means of rivets. The plate H5 and the panel 28 are provided with apertures I38 and I39, respectively, for accommodating the terminals carried by the terminal block I22 whereby the wiring connections may be made atthe rear of the panel 28. The aperture I39 in the panel 28 also accommodates the bellows assembly II6. Preferably,the adjusting nut I24 and the adjustable contact I34 are so adjusted that the switch arm I26 is moved out of engagement with the contact I35 when the high pressure increases to pounds and the switch arm I25 moves out of engagement with the contact I34 when the high pressure increases to pounds.

From the above it is seen that each of the condition responsive control units includes a'plate which is particularly adapted to be mounted on a common control panel, a relatively simple switching mechanism carried by the plate, a relatively simple condition responsive device carried by the plate and terminals electrically connected with the switching mechanism also carried by the plate. This provides an extremely simple basic control unit which may be manufactured in relatively large quantities and readily mounted on a control panel. By manufacturing these different types of control units in large quantities they can be produced very cheaply. Now if it be desired to form a unitary control arrangement, all that is necessary is to select the types of control units desired, mount these control units on a'common panel and electrically interconnect the control units in a manner which will provide the desired control sequence. Such a method of formulating a unitary control arrangement greatly reduces the cost of manufacture.

The starter or relay for controlling the operation of the compressor motor 28 may comprise a plate I 43 suitably mounted to the control panel 28. The various parts of the relay are mounted on the plate I43 so-that a relay unit may be prefabricatedand then secured to the control panel 28. The relay unit may comprise a relay coil I44 for operating an armature I45 which carries switch arms I46, I41, I48, and I49. Upon energization of the relay coil I44 the switch arms I46, I41, I48, and I49 are moved into engagement with stationary contacts I58, I5I', I52, and I53, respectively. If desired the relay or starter unit may include overload cut-out switches generally designated at I54 and I55. These switches may include a thermostatic element I56 anchored at one end by a bracket I51 and operating contacts I58. The bimetallic elements I56 may be heated by heaters I59, the arrangement being such that when the current flowing through the heaters reaches a predetermined high value, the bimetallic elements I56 are flexed to open the contacts I58. Suitable latching mechanism may be provided for maintaining the contacts I58 separated upon the occurrence of element I65 suitably secured to a bracket I66 for operating contacts I61. The bimetallic element I65 is heated by a heater J66, the arrangement being such that when an overload condition occurs, the heater I66 flexes the bimetallic element I65 to open the contacts I 61. Suitable latching mechanism may be provided for required resetting of the switching mechanism upon the occurrence of overload conditions. An operating handle I66 is also provided for manually operating the contacts I 61. The switch 35 which places the control system for the relay or starter "into or out of operation is shown to comprise amanually operated switch arm I12 and a stationary contact I13. The terminal block 36 includes ter-' minals I15andl16, the terminal block-31 includes terminals m, m, and m, and the terminal bloclr. 36 includes terminals I66, III, and

The terminals I11, I16, and I16 of the terminal block 31 are shown to be connected to a threephase source of power. The terminals I66, Ill, and |62 are suitably connected to the compressor motor 26 and the terminals I15 and I16 are suitably connected to the fan motor I4. Whenever switching mechanisms. I54 and I55 are open.

The primary I6l of'the step-down transformer 33 is connected across the terminals I11 and I16 so thatpower is at all times supplied to the stepdown transformer 33.

Closure of the contacts I61 of the combined overload and manual switch-34 completes a cir- V cuit from the secondary I62 through the heater I66, contacts I61, terminal I15, fan motor I4, and terminal I16-back to the secondary I62. Completion of this circuit causes operation of the fans I3 to deliver conditioned air to the space to be conditioned. r If an overload condition exists within the fan circuit the contacts I61 are sepa rated to shut dowri the fan I4 whereby overload I protection'is provided. When the switch arm I12 of the switch 35 engages the contact I13 power is supplied to the operating coil I44 of the relay. 32 and this supply of power passes through .the heater I66 and contacts I61 of the combined manual and overload cut-out switch 34. Therefore if thecontacts I61 are separated, the supply of power to the relay or starter 32 is interrupted even though the switch 35 is'closed. Therefore it is impossible to operate the relay 32 in case the fan motor I4 is not operating.

Assume now that the space temperature rises to {15 to move the switch arms 5| and 52 into engagement with the. contacts 66 and 6i. that the suction pressure increases to pounds to move the switch arms "rand- 66 into engagement with the contacts I66 and Ill and that the high pressure isbelow pounds so that the switch arms I25 and I26 are engaging the contacts I34 and I35, a circuit is completed from the secondary I62 through heater I66, contacts I61,

switch arm I12, contact I13, contact I34, switch arm I25, contact 66, switch arm 5I, contact I66, switch arm 61, switch arm 66, contact I61, switch arm 52, contact 6I', switch arm I25, contact I35, relay coil I44, contacts I56 and bimetallic element I56 of.the overload cut-out switch I55 and contacts I56 and bimetallic element I56 oi the overload cut-out I54 back to thesecondary I62. Completion of this circuit causes energization of the relay coil 44' to pull in the starter or relay ,32 to cause operation of the mechanical refrigerating apparatus. When the starter or relay 32 is thus pulled in, switch arm I46 engages contact I 56 to complete is maintaining circuit for the relay coil I44 which shunts out switch arm 66 and contact I61 of the suction pressure controller, switch arm 52 and contact 6| of the temperature controller 26 and switch arm I26 and contact I35 of the high pressure controller v3i. This maintaining circuit may be traced from the secondary I52 through heater I66, contacts I61, switch arm I12, contact I13, contact'i34, switch arm I25, contact 66, switch arm 5|, contact I66, switch arm 61, switch arm I46, contact I56, relay coil I44,contacts I56, and bimetallic element I56 of the overload cut-out I55, and contacts I56 and bimetallic element I56 of the overload cut-out I 54 back to the secondary I62. Completion of this circuit maintains the relay or starter 32 energized even though the space temperature should drop below 75, or the suction pressure should drop below 50 pounds, or the high pressure should increase above 135 pounds. This maintaining circuit will therefore maintain the refrigerating apparatus in operation until the space temperature shall decrease to the desired value. of 73 whereupon the switch arm 5i is moved out of engagement with the contact 66, or until the suction pressure shall decrease to 20 pounds whereupon the switch arm 61 moves out ofengagement with the contact I66, or until the high pressure increases to pounds whereupon the switch arm I25Tmoves out of engagement with the contact I 34. Whenever any of these last contingencies occur the relay coil I44 is deenergized to drop out the relay or starter '32 and stop operation of the compressor 26. In order to restart the refrigerating apparatus the space temperature vmust again rise to 75 the suction pressure must raise to 50 pounds and the high pressure must decrease to 135 pounds. By reason of the above control arrangement the refrigerating apparatus is operated to maintain the space temperature substantially between 73 and '75 and this operation is protected against current overload conditions in the refrigerating apparatus, high pressure conditions on the'high pressure side of the refrigerating apparatus, and low pressure conditions on the low pressure side of the refrigerating apparatus. Also if the fan motor I4 should be stopped either by manually opening the switch 34 or should be stopped upon the occurrence of overload conditions the refrigerating apparatus is shut down since there is'no need for operating the refrigerating apparatus if the fan'motor I4 is not operating. It is here noted that in order to restart the refrigerating apparatus the suction pressure must raise to some predetermined value, 50 pounds as illustrated,

those skilledin the art upon reference to this specification and therefore this invention is to be limited only by the scope of the appended claims and prior art.

We claim as our invention:

1. In a control system for a mechanical refrigerating apparatus, the combination of, a first control unit including a device responsive to changes in a condition produced by the refrigerating apparatus and a pair of switches scquentially opened and closed thereby, a second control unit including a device responsive to changes in suction pressure of the refrigerating apparatus and a pair of switches sequentially opened and closed thereby, a third control unit including a device responsive to changes in high pressure of the refrigerating apparatus and a pair of switches sequentially opened and closed thereby, a starter for controlling the operation of the refrigerating apparatus, and connections between all of the switches and the starter for starting the refrigerating apparatus when all of the switches are closed and for continuing operation of the refrigerating apparatus as long as one of the switches of each pair is closed.

2. In a control system for a mechanical refrigerating apparatus, the combination of, a first control unit including a device responsive to changes in a condition produced by the refrigerating apparatus and a, pair of switches sequentially opened and closed thereby, a second control unit including a device responsive to changes in suction pressure of the refrigerating apparatus and a pair of switches'sequentially opened and closed thereby, a third control unit including a device responsive to changes in high pressure of the refrigerating apparatus and a pair of switches sequentially opened and closed thereby, a starter for controlling the operation of the refrigerating apparatus, and connections between all of the switches and the starter for starting the refrigerating apparatus when all of the switches are closed and for continuing operation of the refrigerating apparatus as long as one of the switches of each pair is closed, and means for mounting the starter and all of the control units on a common mounting structure to provide a unitary,

control arrangementfor the refrigerating apparatus. 3. In a control system for a refrigerating apparatus having an evaporator for controlling the condition of a medium and an electrically operated mechanism for controlling the circulation of refrigerant throughthe evaporator, the combination of, first and-second switch means, control means responsive to the condition of the medium being controlled by the evaporator for closing the first switch means when the condition rises to a predetermined high value and for opening the second switch means when the condition decreases to a predetermined low value, third and fourth switch means, control means responsive to a condition which is a measure of evaporator temperature for closing the third switch means when the evaporator temperature rises to a predetermined high value and for opening the fourth switch means when the evaporator temperature decreases to a predetermined low value, means for completinga, starting circuit through the first and third switch means to operate the electrically controlled mechanism to start circulation of refrigerant through the evaporator, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, and means for completing a maintaining circuit through the second and fourth switch means and the maintaining switch to maintain the electrically controlled mechanism in operation and circulation of refrigerant through the evaporator, said maintaining switch remaining closed as lbng as the maintaining circuit is completed.

4. In a control system for a refrigerating apparatus having an evaporator for controlling the condition of a medium and an electrically operated mechanism for controlling the circulation of refrigerant through the evaporator, the combination of, first and second switch'means, control means responsive to the condition of the medium being controlled by the evaporator for closing the first switch means when the condition rises to a predetermined high value and for opening the second switch means when the condition decreases to a predetermined low value, third and fourth switch means, control means responsive to a condition which is a measure of evaporator temperature for closing the third switch means when the evaporator temperature rises to a pre determined high value and for opening the fourth switch means when the evaporator temperature decreases to a predetermined low value, fifth and sixth switch means, control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the'fifth switch means when the pressure decreases to a predetermined low value and for opening the sixth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through the first, third and fifth switch means to operate the electrically controlled mechanism to start circulation of refrigerant through the evaporator, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, and means for completing a maintaining circuit through the second, fourth and sixth switch means and the maintaining switch to maintain the electrically operated control mechanism in operation and circulation of refrigerant through the evaporator, said maintaining switch remaining closed as long as the maintaining circuit is completed.

5. In a control system for a refrigerating apparatus having an evaporator for controlling the condition of a medium and an electrically operated mechanism for controlling the circulation of refrigerant through the evaporator, the combination of, first and second switch means, control means responsive to the condition of the medium being controlled by the evaporator for closing the first switch means when the condition rises to a predetermined high value and for opening the second switch means when the condition decreases to a predetermined low value, third and fourth switch means, control means responsive to a condition which is a measure of evaporator temperature for closing the third switch means when the evaporator temperature rises to a predecreases to a predetermined low value, means for completing a starting circuit through the first and third switch means to operate the electrically controlled mechanism to start circulation of .refrigerant through the evaporator, a maintaining switch, means for closing the maintaining switch as an incident to completion of the starting circuit, means for completing a maintaining circuit through the second and fourth switch means and the maintaining switch to maintain the electrically controlled mechanism in operation and circulation of refrigerant through the evaporator, said maintaining switch remaining closed as long as the maintaining circuit is completed, and means for mounting all of the switch means and the control means on a common mounting structure to provide a unitary control arrangement for the refrigerating apparatus.

6. In a control system for a refrigerating apparatus having an evaporator for controlling the condition of .a medium and an electrically oper-' ated mechanism for controlling the circulation of refrigerant through the evaporator, the combination of, first and second switch means, control means responsive to-the condition of the medium being controlled by the evaporator for closing the first switch means when the condition rises to a predetermined high value and for opening the second switch means when the condition decreases to agpredetermined lowvalue, third and fourth switch means, control means responsive to a condition which is a measure of evaporator temperature for closing the third switch means when theevaporator temperature rises to a predetermined high value and for opening the fourth switch means when the evaporator temperature decreases to a predetermined low value, fifth and sixth switch means, control means responsive to the pressure on the high pressure side of the refrigerating apparatus for closing the fifth switch means when the pressure decreases to a predetermined low value and for opening the sixth switch means when the pressure increases to a predetermined high value, means for completing a starting circuit through th first, third and fifth switoh means to operate the electrically controlled mechanism to start circulation of refrigerant through the evaporator, a maintaining switch, means for closing the maintaining switch as ,an incident to completion of the starting circuit, means for completing a maintaining-circuit through the second, fourth and sixth switch means and the maintaining switch tomaintain the electrically operated control mechanism in operationand circulation 'of refrigerant through the evaporator, said main-- taining switch remaining closed as long as the maintaining circuit is completed, and means for mounting all of the switch means and the control means on a common mounting structure to provide a unitary control arrangement for the refrigerating apparatus.

7. In a control arrangement for an air conrefrigerant through the evaporator and air circulating means for circulating air over the evaporator, the combination of, controls means responsivegto the temperature ofgth air, control means responsive'to a condition which is a measure of evaporator temperature,

determined high value and for opening the fourth switch means when the evaporator temperature controlled by both control means for controlling the operation of the mechanism to start circulation of refrigerant through the evaporator only when the temperatur of the air rises to a predetermined high value and the evaporator temperature rises to a predetermined high value and to stop circulation of refrigerant through the evaporator when either the temperatur of the air decreases to a predetermined low value or the evaporator temperature decreases to a predetermined low value, and control means for controlling the operationof the air circulating means.-

said last mentioned control. means also controlling the controlling means to stop circulation of refrigerant through the evaporator when the air circulating means is stopped and to start circulation of refrigerant through the evaporator upon starting of the air circulating means only when the temperature of the air rises to the predetermined high value and the evaporator temperature rises to the predetermined highvalue.

8.. In a control arrangement for an air condi-- orator only when the temperature of the air rises toa predetermined high value, the pressur on the high pressure side decreases to a predetermined. low value and the evaporator temperature increases to a predetermined high value and to stop circulation of refrigerant through th evaporator when either the temperature of the air decreases to a predetermined low value, the pressure on the high pressure side increases to a predetermined high value or the evaporator temperature decreases to a predetermined low value, and control means for controlling the operation of the air circulating means, said last mentioned control means also controlling. the control means to stop circulation of refrigerantthrough the evaporator when the air circulating means is stopped and to start circulation of refrigerant through the evaporator upon starting of the air' circulating means only when the temperature of the air rises to the predetermined high value, the pressure on the high pressure side decreases to the predetermined low value and the evaporatori temperature rises to the predetermined high va ue.

tioning apparatus including a refrigerating apparatus having an evaporator for cooling air and a compressor for circulating refrigerant through the evaporator and air circulating means for circulating air over ,the evaporator, the combina' tion of, control means responsive to the temperature of the air, control means responsive to thepressure' on the high pressure side of the refrigerating apparatus, control means responsive to a condition which is a measure of evaporator temperature, controlling means controlled by all of the control means for controlling the operacontrolling means tion of the compressor to start circulation of refrigerant through the evaporator only when the temperature of the air rises to a predetermined high value, the pressure on the high pressure side decreases to a predetermined low value and the evaporator temperature increases to a predetermined high value and to stop circulation of refrigerant through the evaporator when either the temperature of the air decreases to a predetermined low value, the pressure on the high pressure side increases to a predetermined 10 high value or the evaporator temperature decreases to a predetermined low value, and control means for controlling the operation of the air circulating means, said last mentioned control means also controlling the controlling means to stop circulation of refrigerant through the evaporator when the air circulating means is stopped.

LEO B. MILLER.

WILLIAM L. MCGRATH. 

